1. Field of Invention
The invention relates generally to the field of oil and gas production. More specifically, the present invention relates to an adapter for a shaped charge used in perforating. Yet more specifically, the present invention relates to an adapter for a perforating shaped charge that couples a shaped charge in a perforating gun or tube configured for a different sized shaped charged.
2. Description of Prior Art
Perforating systems are used for the purpose, among others, of making hydraulic communication passages, called perforations, in wellbores drilled through earth formations so that predetermined zones of the earth formations can be hydraulically connected to the wellbore. Perforations are needed because wellbores are typically completed by coaxially inserting a pipe or casing into the wellbore. The casing is retained in the wellbore by pumping cement into the annular space between the wellbore and the casing. The cemented casing is provided in the wellbore for the specific purpose of hydraulically isolating from each other the various earth formations penetrated by the wellbore.
One typical example of a perforating system 4 is shown in FIG. 1. As shown, the perforating system 4 comprises one or more perforating guns 6 strung together to form a perforating gun string 3, these strings of guns 6 can sometimes surpass a thousand feet of perforating length. Connector subs 18 provide connectivity between each adjacent gun 6 of the string 3. Many gun systems, especially those comprised of long strings of individual guns, are conveyed via a conveyance means 5. Examples of conveyances means 5 for deploying or suspending the gun systems within a wellbore include tubing, wireline or slickline.
Included with the perforating gun 6 are shaped charges 8 that typically include a housing, a liner, and a quantity of high explosive inserted between the liner and the housing. When the high explosive is detonated, quickly expanding explosive gases are formed whose force collapses the liner and ejects it from one end of the charge 8 at very high velocity in a pattern called a “jet” 12. The jet 12 perforates the casing and the cement and creates a perforation 10 that extends into the surrounding formation 2. The resulting perforation 10 provides fluid communication between the formation 2 and the inside of the wellbore 1.
A side partial sectional view of a portion of a perforating gun 6 is illustrated in FIG. 2. The perforating gun 6 includes an elongated cylindrical gun body 14 housing a gun tube 16 therein. A shaped charge 8 is mounted in the gun tube 16 generally orthogonal to the tube axis AX. The gun body 14 includes an optional recess 19 aligned with the shaped charge opening 11 to reduce gun body 14 material in the jet 12 path. A lower opening 15 through a portion of the gun body 16 receives the base 9 or closed end of the shaped charge 8. A corresponding upper opening 17 receives the shaped charge 8 open end 11 therethrough; the openings (15, 17) are generally aligned with the shaped charge axis ASC. Shaped charge 8 detonation typically occurs by sending a detonation signal through or along the conveyance means 5 from the surface 13. A firing head 7 receives the signal that responds by igniting a detonation cord 20 that passes through the gun string 3 and connects to each shaped charge 8. Igniting the detonation cord 20 creates a pressure wave that contacts each shaped charge 8 and activates an initiator 21 that in turn detonates the high explosive in the shaped charge 8.
Typically the upper opening 17 in the gun tube 16 is sized to match the shaped charge 8 dimensions. Since shaped charges 8 may be produced in multiple standard sizes, gun tubes 16 having correspondingly sized openings (15, 17) are required for these shaped charges 8. In some instances, operational delays may occur if a properly dimensioned gun tube 16 is not available to accommodate certain sized shaped charges.